Extending the depth of focus of imaging systems is required for various applications, including inter alia medical applications, such as endoscopic system, spectacles, and ophthalmic lenses. Various techniques have been developed to extend the depth of focus of an imaging lens.
For example, the earlier technique developed by the inventor of the present application provides for extending the depth of focus of an imaging lens unit by applying a phase coding to the effective aperture of the imaging lens unit. Various features of this technique are described for example in the following patents and published patent applications: U.S. Pat. Nos. 7,365,917; 7,061,693; US 2009/074239; US 2009/116096; U.S. Pat. No. 7,646,549, all assigned to the assignee of the present application. This technique when utilized in spectacles or ophthalmic lenses may serve as an alternative to the conventional bi- or multi-focal lens approach for patients suffering from presbyopia (i.e. different dioptric powers for distance and reading vision), where desirably extended depth of focus is achieved with the single-focus lens unit.
Various configurations of multi-focal lenses are described for example in the following patents and published patent applications:
U.S. Pat. No. 5,682,223 describes a multifocus, concentric annular ring lens wherein one of the front and back surfaces of the lens defines a central area comprising a circular disc having a spherical surface corresponding to a basic prescription Rx spherical distance optical power. A plurality of annular rings surround the central area and have alternating spherical near and distance optical powers, and at least one intermediate optical power annular ring. The immediate optical power annular ring is located in the middle or outer region of the lens optic zone, and its optical power is intermediate to the distance and near optical powers, to provide visual acuity at intermediate distances. The intermediate optical power annular ring can be placed anywhere in the middle or outer region of the lens optic zone, and can be the second annular ring from the outer edge of the lens optic zone, or can be the outermost annular ring which defines the outer circumference of the lens optic zone. The lens can be a contact lens to be worn on the cornea of the eye, such as a soft hydrogel contact lens, or can be an intraocular lens.
U.S. Pat. No. 5,158,572 describes multifocal lens having a substantially circular central region having a first optical power, surrounded by a plurality of concentric ring regions which alternate between at least two optical powers, one of which may be the first optical power. Preferably, the central region is powered for near vision. For example, one embodiment of the invention is a bifocal lens having a central near-vision portion, a first concentric ring region powered for distance vision, and a second concentric ring region having the same power as the central region.
U.S. Pat. No. 5,198,844 describes a multifocal refractive lens to focus light on the retina of the eye and method of making. The lens is comprised of a plurality of segments, alternating segments having different optical powers, at least for distance vision and another for near. The lens of the invention does not require orientation to produce adequate far and near vision and normal steroscoptic effect. One or both of the segments having the optical powers may have aspherical lens surface. Preferably, the lens has at least one aspherical lens surface and the segments are divided by an arcuate path going from the center of the lens to edge. Such a lens is manufactured by taking lens molds and cutting the molds from the edge through the center to the opposite edge along a predetermined path. The molds are cut so that the segments produced are interchangable and can be fitted together to make a mold that can produce the multifocal refractive contact lens by molding.